KR20070076130A - Information embedding and extracting method for image authentification - Google Patents

Abstract

A method for embedding and extracting information for image authentication is provided to prevent damage of a whole image by dividing an original image into blocks and sub-blocks and embedding authentication information into the sub-blocks, and prevent loss of original data in embedding and extracting authentication information by compensating changed pixel values when extracting authentication information by embedding additional information representing changes of pixel values. An image to which information is embedded, is read and a block counter is set up(S210). The image is divided into K blocks having MxN size(S211). A block counter value is compared with K, the number of the whole blocks(S212). If the block counter value is larger than K, data embedding is terminated(S213). The block is divided into sub-blocks and a sub-block counter is set up(S214). A sub-block counter value is compared with S, the number of whole sub-blocks(S215). If the block counter is smaller than S, the sub-blocks are read(S216). Sub-block samples are aligned and a minimum pixel value is selected(S217). The information to be embedded is encoded(S218). The encoded authentication information is embedded(S219). The embedment of the authentication information is terminated(S220). A differential image is made from an authentication information embedding result(S221). Additional information is embedded into the differential image(S222).

Description

Information embedding and extracting method for image authentification

1 is a conceptual diagram showing information insertion and extraction

2 is an overall flowchart of an information insertion process according to an embodiment of the present invention.

3 is a flowchart for inserting authentication information into a subblock according to an embodiment of the present invention.

4 is a flowchart for inserting additional information according to an embodiment of the present invention.

5 is an overall flowchart of an information extraction process according to an embodiment of the present invention.

6 is a flowchart for extracting additional information according to an embodiment of the present invention.

7 is a flowchart for extracting authentication information from a subblock according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of inserting and extracting information for authentication into image data, and more particularly, to a lossless data embedding method in which no loss of original data occurs during insertion and extraction of information. will be.

The popular dissemination of computers and the rapid development of networks have enabled the free exchange and easy access of various kinds of multimedia contents. However, easy access to a variety of data has led to problems related to the illegal copying of indiscriminate digital content. Due to illegal copying and distribution of music, photographs, and even high-definition videos, many problems related to intellectual property arise. Illegal copying and distribution of digital contents is a very important problem that causes the author to lose his creative will and serious economic loss. Therefore, copyright protection technology is required to prevent illegal duplication without the owner's consent and effectively protect the ownership.

As a technology for protecting digital data, many access control technologies using encryption techniques and firewalls have been developed. However, encryption-based methods have the possibility of information leakage such as key exchange, and may be decrypted through numerous attempts. And since the encrypted information has a completely different nature from the original information, it is also easy to know whether encryption has been performed. Access control using a firewall can not exclude the possibility of illegal digital content distribution by an authorized user. Therefore, it is difficult to effectively protect copyright and ownership by using such technology in the rapidly growing contents market and e-commerce.

Digital content copyright protection technology solves the problems caused by indiscriminate copying of digital content and provides technical protection measures to obtain legitimate copyright protection. There are many types of products that provide such technical protection, but they can be classified into two categories: active (Explicit) content and passive (Implicit) content protection.

Active content protection is a technology that restricts the use of content, which defines usage rules and ensures that content is used only within its scope. Representative technology is DRM (Digital Rights Management).

Passive content protection does not restrict the use of the content, but is a technique for securely displaying the copyright holder's information or the user's information. Typical technologies include watermarking, DOI, and INDECS.

A watermark is a word meaning transparent picture or writing used when sending a cipher text in a medieval church. It originated from marking water on one's own work by using water or medicine that can only be seen in a special way.

Digital watermarking is a technology of inserting specific information as shown in FIG. 1 so that the human eye cannot discriminate data capable of authenticating copyright in digital content such as documents, audio, images, and video. When there is a dispute over intellectual property rights in the distribution of contents, it is possible to protect its copyright by extracting a watermark inserted in the contents and verifying the owner.

The watermark must meet the following requirements.

First, there must be robustness. The watermarking information inserted in the original image has an extractable property without being damaged in any case. By using this feature, even if the watermarked image is output to a printer, watermarking information can be extracted from the printed matter, thereby identifying who the copyright holder of the corresponding content is.

Second, there must be fragility. The watermarking information is easily discarded when the image in which the watermarking information is inserted is deformed. By using these characteristics, it is easy to find out whether the deformation is possible, so it can be applied to the same field as the original proof. For example, consider printing and distributing documents that require original proof. If the fragile watermarking information is inserted and distributed in the printout, the watermarking information will be lost while copying it to the copier. Therefore, it is possible to mask the authenticity of the original document by determining the existence of watermarking information.

The third requirement is Fingerprinting Watermarking. It uses the property to insert and extract various invisible information in the original image. This technology can be applied to the field of illegal use tracking of the content because it can store the user's information and usage history when the user accesses the content. However, even in this case, as in the case of robust watermarking, it is not only able to satisfy the charging agent that the watermarking module should be installed in all terminals, and there is no problem in using the contents even without the watermarking module, so it is questionable about its utility. Still exists.

In recent years, attention has been focused on technologies for protecting copyrights effectively by inserting ownership information into digital content itself to prevent illegal copying or distribution. This technique is called Information Hiding.

Existing methods of information hiding have caused loss of information during the insertion and extraction of information. Considering that the change occurring in the least significant bit of each pixel in the 8-bit gray image is less noticeable to the human, there is a method of inserting encrypted binary information after setting the least significant bit plane of the image to zero. However, this loss of information can cause serious problems in areas such as medical imaging and military imaging.

An object of the present invention is to provide a lossless information embedding and extraction method that does not cause loss of original data during insertion and extraction of information.

In addition, an object of the present invention is to increase the reliability of the restored information by determining whether distortion is generated through authentication of the restored original information based on the proposed lossless information concealment technique.

In addition, the present invention is to provide a method that can use the authentication information as a medium for transmitting important information by performing encryption (Encryption) on the information to be inserted to protect the authentication information itself inserted in the image when the information is inserted The purpose.

Another object of the present invention is to provide a method of locally detecting a region in which distortion or manipulation of an image occurs by dividing an entire image into a plurality of blocks and inserting authentication information into each block.

Information hiding method according to the embodiment of the present invention,

Dividing the image into a plurality of blocks;

Dividing the divided blocks into subblocks;

And inserting an authentication supplement into one pixel of each of the divided subblocks.

In the present invention, the step of inserting the authentication information is characterized in that the insertion into the pixel having the minimum pixel value of the sub-block.

In addition, in the present invention, the block is characterized in that divided into 2 × 2 subblocks.

In addition, the information hiding method according to an embodiment of the present invention, characterized in that it further comprises the step of encrypting the authentication information to be inserted.

In the present invention, the authentication information is characterized in that the binary information.

In addition, the information hiding method according to an embodiment of the present invention, characterized in that it further comprises the step of generating additional information corresponding to the change in the pixel value according to the insertion of the authentication information.

In the present invention, the generating of the additional information may include generating 1 when a change occurs in the pixel value into which the authentication information is inserted, and generating 0 when there is no change in the pixel value.

In the present invention, the generating of the additional information may include generating the additional information 0 without changing the pixel value if the pixel value into which the authentication information is inserted is odd and the authentication information to be inserted is 1, and the pixel value being inserted is odd. When the authentication information to be inserted is 0, the pixel value is decreased by 1 and the additional information 1 is generated.

Also, in the present invention, the generating of the additional information may include generating the additional information 0 without changing the pixel value if the pixel value into which the authentication information is inserted is an even number and the authentication information into which the information is inserted is 0 and the inserted pixel value is even. If the authentication information to be inserted is 1, the pixel value is decreased by 1 and the additional information 1 is generated.

In addition, the information concealment method according to an embodiment of the present invention comprises the steps of: obtaining a difference image using the difference of adjacent pixels from the image inserted the authentication information;

Inserting additional information into the difference image; It characterized in that it further comprises.

In addition, the method of extracting hidden information according to the embodiment of the present invention,

Dividing the image into a plurality of blocks;

Dividing the block into subblocks;

And extracting authentication information from the subblock to restore the original image.

In addition, the method for extracting hidden information according to an embodiment of the present invention may further include obtaining a difference image from the image and extracting additional information therefrom.

In the present invention, the step of extracting the authentication information is characterized in that the extraction using the additional information.

In addition, the method for extracting hidden information according to an embodiment of the present invention may further include decrypting the encrypted authentication information.

In the present invention, the additional information is characterized by extracting 1 when there is a change in the pixel value in which the authentication information is inserted, and extracting 0 when there is no change in the pixel value in which the authentication information is inserted.

Further, in the present invention, the additional information may be an odd pixel value of the subblock in which the authentication information is inserted and the inserted authentication information is 1, or the pixel value of the subblock in which the authentication information is inserted is an even number and the inserted authentication information is 0. It is characterized in that 1 is extracted.

Further, in the present invention, the additional information may be an odd pixel value of the subblock in which the authentication information is inserted and the inserted authentication information is 0, or a pixel value of the subblock in which the authentication information is inserted is even and the authentication information inserted is 1 In this case, 0 is extracted.

In the present invention, when the additional information is 1, the original image is reconstructed by increasing the pixel value of the subblock in which the authentication information is inserted by one.

In the present invention, when the additional information is 0, the original image is reconstructed without changing the pixel value of the subblock in which the authentication information is inserted.

Hereinafter, with reference to the accompanying drawings will be described in detail.

2 is an overall flowchart of authentication information insertion according to an embodiment of the present invention.

First, an image to insert information is read and a block counter BC is set (S210). The image is divided into K blocks having a size of M × N (S211).

When the block counter BC compares the entire blocks K (S212) and the block counter value is larger than K, data insertion is terminated (S220). When the block counter value is less than K, one block is read and a block counter block counter is read. Increase one (S213). Next, the block is divided into subblocks and a subblock counter SBC is set (S214). At this time, the subblocks have a size of 2 × 2 and the number of divided subblocks is expressed as S.

The subblock counter is compared with the total number of subblocks S (S215). If the block counter is large, the process returns to the step S212 of comparing the block counter with the number of blocks K. If the SBC is small, the block is read. After S216, the subblock samples may be aligned, a minimum pixel value may be selected (S217), and the information to be inserted may be encrypted for protection of the authentication information itself (S218). The encrypted authentication information is inserted (S219). At this time, a change occurs in the pixel value depending on whether the inserted information is 0 or 1, and additional information for determining whether the pixel value is changed is stored in a buffer. The subblock counter is incremented by one.

The summary of the insertion process of the authentication information and the additional information and the change of the pixel value will be described. The logo information for authentication is inserted into each block after dividing one image into K blocks. In this case, the size of one block is 2M × 2N when the logo information to be inserted is a M × N binary image. This is because one binary information is next inserted for a 2x2 subblock. Therefore, one block is divided into M × N subblocks again.

Insertion of information at the subblock level is performed as follows. The four pixels constituting the 2x2 block are arranged in order from largest to smallest, and then the corresponding information is inserted into the pixel having the smallest value.

As the above procedure, the procedure of inserting authentication information is terminated (S220), and a procedure for inserting the additional information is performed.

That is, a difference image is generated from the authentication information insertion result (S221), and additional information is inserted into the difference image (S222).

In detail, in order to insert additional information, a space for inserting additional information is created using a differential image technique. The difference image is a difference image of an image obtained by obtaining a difference with respect to pixels of corresponding positions for two sub-images formed by decomposing one image into odd and even lines.

By inserting the additional information as described above, the information hiding procedure is terminated.

3 illustrates a process of inserting information into a subblock according to an embodiment of the present invention.

As described above with reference to FIG. 2, after the pixel values of the subblocks are aligned, the minimum pixel value is selected, and it is determined whether the selected minimum pixel value is an odd number (S314).

If the determination result is odd, it is determined whether authentication information to be inserted, that is, binary data is 1 (S315). If the data to be inserted is 1, the additional information 0 is inserted without any change to the selected minimum pixel value (S316). If the data to be inserted is not 1, 1 is subtracted from the selected minimum pixel value and the additional information 1 is inserted (S317). .

If the pixel value is an odd number, it is determined whether authentication information to be inserted, that is, binary data is 0 (S318). If the binary data is 0, the additional information 0 is inserted without any change in the selected minimum pixel value (S319). If the binary data to be inserted is not 0, 1 is subtracted from the selected minimum pixel value and the additional information 1 is inserted (S317). .

In the above procedure, authentication information is inserted and additional information according to whether the pixel value is changed is stored in the buffer (S320).

The summary of the above process is as follows.

If the pixels constituting the 2x2 subblock are A, B, C, D and the size of the pixel value is defined as A≥B≥C≥D, the pixel having the smallest value is D.

If the information to be inserted is 1 and D has an odd value, no change occurs in the value of D. However, if D is even, it is reduced by one from the value of D. The case where a value of 0 should be inserted is as follows. If D is even, there is no change in the value of D. However, if D is odd, the value of D is decreased by one. This is summarized in Table 1.

Information to insert The value of pixel D The value of the changed pixel D 0 odd number D-1 0 Even D One odd number D One Even D-1

E.g,

I) If A = 115, B = 103, C = 99, D = 81 and the information to be inserted is 0, then D = 80.

Ii) If A = 115, B = 103, C = 99, D = 80 and the information to be inserted is 1, then D = 79.

In this way, the information of the 2x2 blocks is combined to generate a block in which the authentication information is inserted. At this time, additional information for informing whether a change occurs or no change occurs in the value of D is stored in a buffer.

4 is a flowchart illustrating a process of inserting additional information according to an embodiment of the present invention in detail.

First, read the image (S410) to create a differential image (S411). As discussed above, the difference image may be obtained by using a difference for pixels of corresponding positions for two sub-images formed by decomposing one image into odd and even lines.

In the difference image, a histogram is made with the difference value as the X axis and the samples corresponding to the X axis, that is, the number of pixels in the difference image as the Y axis (S412). If the difference is listed and counted in the difference image, the maximum value is obtained at the point where the difference value is 0, and the histogram can be obtained because the Gaussian distribution scattered from both sides is displayed based on the difference value.

The histogram is moved to insert additional information in the histogram (S413). Looking at the moving method in detail, the histogram has a maximum value at the difference value 0 and a second and third maximum values at the difference values -1 and +1 and inserts information using the same. For example, all the left difference values are shifted from the difference value -2 by -1 to insert information using the difference value -1 on the left side of the difference value 0. By doing this, we can leave the position of -2. Similarly, the right side with respect to 0 can be emptied of +2 by moving all right values by +1 with respect to +2.

After the histogram is moved, the additional information counter ALC is set to 0 and the total number of additional information is set to TA (S414).

If the additional information counter is 0, the first additional information is read and if not, the next additional information is read (S415).

It is determined whether the additional information is 1 (S416), if 1, the additional information is inserted into the empty place of the histogram (S417), and the additional information counter is incremented by one. If the additional information is not 1, the additional information is inserted into the empty place of the histogram. It increments one additional information counter without a process (S419). Looking at the process of inserting additional information in detail, when the information to be inserted is 1, it adds +1 to the Y-axis corresponding to the vacant position and adds -1 to -1 from the difference value of X-axis and -1 to -1 without changing the overall data. You can insert information. Also, when the information to be inserted is zero, there is no change in the histogram. By securing a space for creating additional information, the original pixel values described above can be found.

If the additional information counter ALC is smaller than the total number of additional information, the additional information is read again (S415), and the procedure is performed. If the additional information counter ALC is larger than the total number of additional information, the procedure is terminated.

In the above, the process of inserting authentication information according to an embodiment of the present invention has been described. Hereinafter, a process of extracting the insertion information will be described.

5 is an overall flowchart illustrating a process of extracting embedded authentication information according to an embodiment of the present invention.

The inserted information may be extracted by performing the insertion process of FIG. 2 in a reverse process.

Looking in detail, first read the image (S510) to create a differential image (S511). Since the method of making the difference image has been described above, it is omitted.

The additional information inserted from the difference image is extracted (S513). The extraction of the additional information is shown in detail in FIG. 6.

By extracting the additional information, an image into which authentication information is inserted can be obtained. The image from which the additional information is extracted is divided into K blocks having an M × N size (S514). At this time, the block counter BC is set to zero.

The block counter BC is compared with the number K of blocks (S515). If BC is large, the procedure ends. If BC is small, one block is read and the block counter BC is increased (S516).

The block is divided into S subblocks having a size of 2 × 2 (S517). At this time, the subblock counter SBC is set to zero.

It is determined whether the subblock counter SBC is smaller than the number S of the entire subblocks (S518). If SBC is large, the control returns to the block counter comparison unit S515, and if the SBC is small, the SBC-th block is read (S519).

The authentication information is extracted using the additional information, and the original image is restored (S520). The authentication information extraction process is shown in detail in FIG. 7.

If the extracted authentication information is encrypted (S521), the subblock counter SBC is incremented by 1 (S522), and the process returns to step S518, where the procedure is repeated.

An additional information extraction process will be described with reference to FIG. 6.

As described in FIG. 4, the image is read, a differential image is generated, and a sample having a difference value of 0 or ± 2 is found (S613). At this time, the sample value counter TS having ± 2 is set to the number T of samples of ± 2 found above. As described in the additional information insertion process, when the difference value is 0, additional information is inserted at the position where the difference value is 0, and when the additional information is 1, the histogram is moved and the additional information is positioned at the difference value ± 2. Since we insert, we find a sample with a difference of 0 or ± 2 to extract it.

A sample having an absolute value of the difference value of 0 or 2 is obtained (S614), and the sample value counter determines whether the TS is 0 (S615).

If the sample value counter TS is 0, the procedure is terminated. Otherwise, it is determined whether the absolute value of the difference value is 0 (S616). If the difference value is 0, additional information 0 is extracted (S617). If the difference value is not 0, it is determined whether the absolute value of the difference value is 2 (S618), and if the absolute value is 2, The histogram is moved and the additional information 1 is extracted (S619). If the absolute value is not 2, the histogram is moved without extracting the additional information (S620). The histogram movement is for restoring the movement made when the additional information is inserted.

After performing the procedure, the sample value counter TS is decremented by 1 (S621), and again, it is determined whether the sample value counter TS is 0 (S615), and the above procedure is performed again.

A process of extracting authentication information from a subblock will be described with reference to FIG. 7.

First, as described in the entire flowchart of the extraction process of the authentication information of FIG. 5, additional information may be obtained by reading a 2 × 2 subblock, aligning four pixels, and selecting a minimum pixel value (S710 to S712). .

It is determined whether the selected minimum pixel value is an odd number (S713). As a result of the determination, if the pixel value is an odd number, authentication information 1 is extracted (S714) and it is determined whether the additional information is 1 (S716). If the pixel value is an odd number, authentication information 0 is extracted (S715) and it is determined whether the additional information is 1 (S716).

If the additional information is 1, the original image is restored by increasing the pixel value by 1 (S717). If the additional information is not 1, that is, 0, the original image is restored without changing the pixel value (S718). If the additional information is 1 when inserting the authentication information, the insertion pixel value has changed, so that the value is increased to restore this value. However, if the additional information is 0, the insertion value is inserted without any change in the pixel value. Does not occur.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, the scope of the present invention is not limited thereto and is determined by the appended claims, and has a general knowledge in the art to which the present invention belongs. If it can be carried out by variously changed and substituted within the scope without departing from the spirit and the appended claims of the present invention.

According to the present invention, when the authentication information is inserted, the original image is divided into blocks and subblocks, and the authentication information is inserted into the subblocks, thereby inserting the information into each block, even when someone manipulates a specific block. Only the data in the file is damaged and the entire image is protected from being damaged. That is, according to the present invention, locality is ensured.

In addition, according to the present invention, by inserting additional information indicating whether or not the pixel value changes when the authentication information is inserted and using the extracted information, it is possible to compensate for the changed pixel value even when extracting the authentication information. Therefore, according to the present invention, there is an effect that the loss of original data does not occur during the insertion and extraction of authentication information.

In addition, according to the present invention, it is possible to increase the reliability of the restored information by determining whether distortion is generated through authentication of the restored original information based on the proposed lossless information concealment technique.

In addition, according to the present invention, by encrypting the information to be inserted in order to protect the authentication information itself inserted into the image when the information is inserted, there is an effect that the authentication information can be used as a medium for transmitting important information. .

Claims (19)

Dividing the image into a plurality of blocks; Dividing the divided blocks into subblocks; And inserting an authentication supplement into one pixel of each of the divided sub-blocks. The method of claim 1, wherein the inserting of the authentication information comprises inserting into the pixel having the minimum pixel value among the subblocks. The method of claim 1, wherein the block is divided into subblocks of size 2x2. The method of claim 1, further comprising encrypting authentication information to be inserted. The method of claim 1, wherein the authentication information is binary information.  The method of claim 1, further comprising generating additional information in response to a change in a pixel value according to the authentication information insertion. The information generating method of claim 6, wherein the generating of the additional information comprises generating 1 when a change occurs in a pixel value into which authentication information is inserted, and generating a 0 when there is no change in the pixel value. Insert method. The method of claim 6, wherein the generating of the additional information comprises generating the additional information 0 without changing the pixel value if the pixel value into which the authentication information is inserted is odd and the authentication information to be inserted is 1 and the pixel value inserted is odd. And if the authentication information to be inserted is 0, decreasing the pixel value by one and generating additional information 1. The method of claim 6, wherein the generating of the additional information comprises generating the additional information 0 without changing the pixel value if the pixel value into which the authentication information is inserted is even and the authentication information into which the authentication information is inserted is 0. And if the authentication information to be inserted is 1, decreasing the pixel value by 1 and generating additional information 1. The method of claim 6, further comprising: obtaining a difference image by using a difference of adjacent pixels from the image into which the authentication information is inserted; Inserting additional information into the difference image; Information insertion method further comprises a. Dividing the image into a plurality of blocks; Dividing the block into subblocks; Extracting authentication information from the subblock and restoring an original image. 12. The method of claim 11, further comprising obtaining a differential image from the image and extracting additional information therefrom. The method of claim 12, wherein the extracting the authentication information comprises extracting the additional information using the additional information. 13. The method of extracting hidden information according to claim 11 or 12, further comprising decrypting the encrypted authentication information. The method of claim 12, wherein the additional information extracts 1 when there is a change in the pixel value into which the authentication information is inserted, and extracts 0 when there is no change in the pixel value into which the authentication information is inserted. . The method of claim 12, wherein the additional information includes an odd pixel value of a subblock in which authentication information is inserted and an embedded authentication information is 1 or a pixel value of a subblock in which authentication information is inserted is an even number and embedded authentication information is 0. Concealed information is extracted. 13. The method of claim 12, wherein the additional information includes an odd pixel value of a subblock into which authentication information is inserted and an embedded authentication information is 0, or a pixel value of a subblock into which authentication information is inserted is an even number and embedded authentication information is 1. Concealed zero is extracted. The method of claim 12, wherein when the additional information is 1, the original image is restored by increasing the pixel value of the sub-block in which the authentication information is inserted by one. The method of claim 12, wherein when the additional information is 0, the original image is reconstructed without changing the pixel value of the subblock into which the authentication information is inserted.

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